I struggle to grasp vanAmsen's concise O(1) space complexity algorithm. I've utilized the following visualization to analyze each step systematically to comprehend it fully.

Key Points:

1. advance the current node to the right by:
 (1) adjusting the current.next pointer
2. put next_node all the way left to pre.next by
 (2) updating pre.next pointer
 (3) updating next_node.next pointer

class Solution:
    def reverseBetween(self, head: Optional[ListNode], left: int, right: int) -> Optional[ListNode]:
        if not head or left == right:
            return head
        
        dummy = ListNode(0, head)
        prev = dummy
        
        for _ in range(left - 1):
            prev = prev.next
        
        current = prev.next
        
        for _ in range(right - left):
            next_node = current.next
            current.next, next_node.next, prev.next = next_node.next, prev.next, next_node

        return dummy.next